Using Pulsars to probe the interstellar medium

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Using Pulsars to probe the interstellar medium. Barney Rickett, University of California San Diego Department of Electrical & Computer Engineering. Presentation at PAC 2012 - KIAA/PKU October 2012. Probing the Galaxy with Pulsars big picture. - PowerPoint PPT Presentation

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<ul><li><p>Using Pulsars to probe the interstellar mediumBarney Rickett, University of California San DiegoDepartment of Electrical &amp; Computer EngineeringPresentation at PAC 2012 - KIAA/PKU October 2012</p></li><li><p>Probing the Galaxy with Pulsarsbig pictureFAST sensitivity and sky coverage =&gt; More pulsars and DMs (DM = ne dl)Pulsar HI absorption measurements =&gt; new pulsar distancesMore pulsars, DMs &amp; distances =&gt; Better model for electron distribution in Galaxy=&gt; Better model for 3D distribution of pulsarsPulsar Rotation Measures + better electron model=&gt; Better model for Galactic Magnetic Fields</p></li><li><p>DM sin(b) versus Latitude bassume stratified disk =&gt; electron density ne(z)DM = Lp ne dl = Zp ne(z) dz/sinbDM sinb = Zp ne(z)dz if Zp &lt; Hne DM =&gt; Lp ne(0) Lp if Zp &gt; Hne DM sinb =&gt; DM90 = ne(z)dz ~ ne(0) Hnene(z)zHneLpZp**</p></li><li><p>DM versus Latitude bDM = ne dl = ne(z)dz/sinb &lt; DM90 /sinb</p></li><li><p>DM sin(b) versus LatitudeDM sinb = Zp ne(z)dz &lt; DM90</p></li><li><p>Delay spectrum (Jenet et al. 2010) PSR B1937+21 Possibility to determine the temperature and number of cool HI clouds.emission</p><p>absorption</p><p>delay</p></li><li><p>H-a Galactic DistributionSMC LMC Ia ~ ne2 dl = EM (cm-6 pc)Large Ia can be a lower bound to EM (due to saturation) Cygnus Region</p></li><li><p>Pulsar DMs + Galaxy Ha </p></li><li><p>Zoom Pulsar DMs + Galaxy Ha </p></li><li><p>Zoom2 Pulsar DMs + Galaxy Ha </p></li><li><p>Probing the Galaxy with PulsarsModelling the electrons in the Galaxy:Taylor &amp; Cordes 1993; Cordes &amp; Lazio 2001-2006Questions:Are pulsars concentrated in spiral arms?At 100 km/sec a psr moves 1kpc in 107 yearsIs the concentration of psrs near 40deg longitude:a spiral arm? or due to AO observational (sensitivity) biasWhat is ne between the spiral arms? Are there more pulsars hidden by scattering in the Cygnus region?Better estimates of the perpendicular distribution of pulsars &amp; electron density </p></li><li><p>Spiral structure42 degCordes &amp; Lazio 2006</p></li><li><p>Cordes Lazio Ne model (~2006)Need to comparedistributions of Plasma and Pulsars </p><p>Neutron star distribution as history of star formation ?</p></li><li><p>FAST simulationSmits et al. </p></li><li><p>Probing the Galaxy with Pulsarssmall-scale pictureSmall-scale structure in the ISM scatters radiowavesRefractive index deviation l2Scattering is typically consistent with Kolmogorov turbulence over scales from 1000 km -&gt; 100 AU (Armstrong et al. 1995)But turbulence level is very inhomogeneous i.e. patchy see the Ha mapsTurbulence is often anisotropicProbe by pulsar scattering:DM variationPulse Broadening time &amp; ISS bandwidthScattering hides pulsars (esp. MSPs) Scintillation Arcs (Stinebring et al.)</p></li><li><p>ISS GeometryFrom Radio Galaxy Quasar or AGN2000pc</p></li><li><p>Structure function of Dispersion Measure PSR B1937+21Ramachandran et al. 2006</p></li><li><p>Temporal broadeningqzoscattering layerScattered Pulse shape: P(t) = 02B[q=(2ct/zeff),b] db zeff = (zo+zp)(zp/zo)</p><p>Pulse Broadening time tscatt = zeff q2 /2c f -4.4zppulsarScattered Image Brightness = B(q,b)</p></li><li><p>Pulse Broadening vs frequency</p></li><li><p>Scattered pulse shape for PSR J1644-45 observed at 660 MHz at ParkesRickett, Johnston and Tomlinson, 2004Detailed shape is a diagnostic of scattering at high wavenumbers (ie due to very small scales)Conclude linner ~ 75 km Allowing for anisotropy makes this a lower limit</p><p>This requires very high signal to noise ratio (ie FAST)loge[P(t)]Kolmogorov:Inner scale &lt; 10kmInner scale &gt; 1000km</p></li><li><p>tscatt versus DM The uniform Kolmogorov model predicts: tscatt DM2.2 But the observations show a much steeper dependence on DM. They imply that at larger distances through the electron layer, there is an increasing chance of encountering regions of high density and high turbulence. </p><p>This result is built in to the Galactic electron model of Cordes &amp; Lazio (2003) as a high level of patchy turbulence in the inner GalaxyNote that tscatt responds to a column of density-variance (related to emission measure). Since we expect dne ~ne , tscatt picks out the highest densities along a line of sight. </p></li><li><p>PSR B1133+16 at Arecibo(Stinebring et al.)Secondary Spectrum (S2) with three scintillation arcsdtdPrimary Dynamic SpectrumScintillation Arcstscatt = 1/(2 dnd)</p></li><li><p>The Puzzle of the Arc-letsHill, Stinebring et al. (2005) showed this example of the arcs observed for pulsar B0834+06. In addition to the main forward arc (following the dotted curve) there are reverse arclets. Those labelled a-d are particularly striking. </p><p>They observed them over 25 days and found that they moved in Delay and Doppler, precisely as expected for the known pulsar proper motion. </p></li><li><p>The Puzzle of the Arc-lets 2The left plot shows the angular position of the structures (in mas) responsible for each reverse arclet, mapped from the Doppler frequency fD . The lines have the slope expected for the known pulsar proper motion.The right plot shows how fD varies with observing frequency. </p><p>Remarkably this shows that the spatial location of the scatterers is independent of frequency. They DO NOT show the expected shift due to the dispersive nature of plasma refraction.Predicted for plasma refraction334 MHz321 MHzDoppler Frequency fD (mHz)</p></li><li><p>VLBI of Scintillation Arcs (Brisken et al 2010)</p></li><li><p>Scattered Brightness from B0834+06 Scattered image reconstructed by mapping from the secondary spectrum. The phase provides orientation in RA/Dec(J-J Gao PhD UCSD)DqRA (mas)Dqdec (mas)</p></li><li><p>Walkers decomposition of Hill/Stinebring observations of B0834+06 327 MHz Arecibo Imaged by Gao assuming VpsrBlue line shows the axis derived from VLBI by Brisken, Gao et al. </p><p>Scattered Brightness is Anisotropic, Asymmetrical &amp; Intermittent Doppler Frequency fD (mHz)</p></li><li><p>What do arcs tell us?New tool for study of ISM Thin screen model is often remarkably successful =&gt; ISM is patchy</p><p>Examples of thin arcs and multiple reverse arclets require: a) Highly anisotropic scattering b) very patchy distribution of turbulence Intense turbulent regions ~10 AU dominate in a path of 108 AU !</p><p>Together these upset the assumptions of isotropy and uniformity in a turbulent &amp; ionized ISM. Instead we have anisotropy and intermittency in the turbulence.</p><p>It leaves us with fascinating puzzles:What are the astro-physical sites that cause peaks in the scattering?What is the cause of the 1-D fine structure ? What role for magnetic field?What consequences for MSP timing ?</p><p>New ideas from Cyclo-Stationary spectral analysis New facilities GBT, EVLA, LOFAR, FAST</p></li><li><p>SummaryThe sensitivity of the FAST telescope will explore the ISM on the large scale:Spatial distribution of Pulsars Inside and outside of spiral armsMore associations with supernova remnantsNew distance measurements by sensitive HI absorptionDelay spectrum as a new probe of HINew DMs improve the modelling of plasma in the Galaxy (Ne2020?) What ionizes the ISM?Influence of HII regions and supernova remnantsNew Rotation Measures improve knowledge of the Galactic Magnetic FieldRM from pulsars, extra-galactic sources and diffuse synchrotron emission</p><p>Scattered pulse shapes and secondary spectra will explore the ISM on the small scale: Monitoring the non-uniform ISM for corrections to pulsar timingDM variation of MSPs for timing correction Particular discrete regions of scatteringWhat is their physical origin?What is their density in interstellar space? Study of turbulence in the interstellar plasma</p></li><li><p>Planck map</p></li><li><p>PSR B1737+13 mjd 53857 Arecibo 320 MHz StinebringIn the 1-D scattering we find secondary spectrum: S2(t,fD) B(t/AfD+AfD) x B(t/AfD-AfD) / |fD|in terms of the 1-D brightness function B(q) and a scaling constant AHence from observations of S2 one can fit the observations S2 to a 1-D model and so estimate B(q)</p></li><li><p>PSR B1737+13 mjd 53857 Arecibo 320 MHz Stinebring</p></li><li><p>PSR B1737+13 mjd 53857 1700 MHz 1-dim Scattered Power</p><p>Scattered Brightness is Anisotropic, Asymmetrical &amp; Intermittent</p></li><li><p>Secondary spectrum theory 1I = |E1 + E2|2 if E1 and E2 are coherent at frequency n: = |E1|2 + |E2|2 + 2E1E2cos(Df)where Df = 2(n1t1-n2t2)+f01-f02t1 = t+dt1, n1 = n+dn1Df = 2[n(dt1- dt2)+(dn1- dn2)t .. + ..O(dn,dt) + f01-f02]wheredt1 = zq12/2c is the relative time delaydn1 = n(V.q1)/c is the relative Doppler frequencyVscattering screen</p></li><li><p>Arc Equations scattering screent = dt1- dt2 = [q12- q22] (z/2c)fD = dn1- dn2 = (q1x- q2x)V/lWith q2 fixed there is a quadratic relation between t and fD which depends on q1y2. If in addition q1x and q1y lie on a straightline (ie 1-D scattered brightness) the relation is a parabola through the origin =&gt; reverse arcletbIn that case the visibility phase on baseline b corresponds to the mean position of the two angles =&gt; (q1+ q2). b/lApex of parabola is where q2=0, hence visibility phase at an apex gives astrometric measure of q1.</p></li><li><p>B1737+13 10-weeks of 1-D modelsProper motion ~30 mas/yr</p><p>Psr distance 4.8 kpc (DM)</p><p>Angle units ~ mas</p><p>Proper motion predicts 0.5 mas per week</p><p>No coherent shifts seen</p><p>Some decorrelation even over half-hour</p></li><li><p>Alternative Geometries for ArcsPerpendicular GeometryAnisotropic &amp; intermittent - spaghetti-like filaments in SN remnantsSeparate offset feature also neededParallel GeometryIsotropic scatterers clumped linearlyOther clumps too far from line of sightIndividual scattering centersBackground of distributed turbulence</p></li><li><p>Part of Cygnus Loop Supernova Remnant age 5-10 KyrBright shell:EM ~ 100 pc cm-3dL ~ 1 pc=&gt; max ne ~ 10 cm-3 ~4 pc</p></li><li><p>Density of Galactic plane pulsars vs longitudeHa intensity 5 deg latitude</p><p>4 quadrants lower DM toward anticenter</p></li></ul>